1. Field of the Invention
The present invention generally relates to a drive control device of a rotation member, a method for drive control of the rotation member and an image forming apparatus including the drive control device. More particularly, the disclosed invention relates to a drive control device for appropriately rotating an endless belt member or an electrophotographic photoreceptor, a method for drive control of the same and an image forming apparatus, such as a copier, a printer, or a facsimile machine, which includes the drive control device.
2. Description of the Related Art
Recently, the number of image forming apparatuses such as copiers, printers, etc, that are able to form full-color images using electrophotographic technology, has been increasing along with demand from the market for such apparatuses.
Some of these electrophotographic image forming apparatuses have a plurality of image development devices around a single electrophotographic photoreceptor. In such image forming apparatuses, each of the plurality of image development devices has a respective single-color toner. In addition, this type of image forming apparatus forms a color image by attaching the respective single-color toner onto the latent image on the electrophotographic photoreceptor, and transfers the color image formed on the electrophotographic photoreceptor to the intermediate transferring belt. The full-color image formed on the intermediate transferring belt is then transferred onto a recording medium such as paper or a paper like medium.
Another type of electrophotographic image forming apparatus, called a tandem electrophotographic image forming apparatus, has a plurality of image generation units each comprising an electrophotographic photoreceptor and an image development unit placed in alignment. Each of the image generation units generates a single-color image with respective color toner. In this type of image forming apparatus there are two methods by which the single-color image is transferred onto the recording medium so as to generate a full-color image. One is entitled the “direct transferring method”. In this method, every single-color image is successively transferred onto the recording medium, which is supported and delivered by a sheet delivering belt, so as to form a full-color image on the recording medium. The other method is entitled the “indirect transferring method”. In this method, every single-color image is successively transferred onto an intermediate transferring belt so as to first form a full-color image on the intermediate transferring belt, then the full-color image is transferred onto a recording medium by a second transferring unit.
In such a color image forming apparatus, multiple color toner images, such as yellow, cyan, magenta, and black, are formed and are successively superimposed by being transferred onto a recording medium or an intermediate transfer belt so as to form a full-color image. As a result, if a displacement of the superimposing position of the multiple color toner images were to occur, color drift or change in color, which degrades the image quality of the full-color image may occur. Therefore, it is important to ensure that the superimposing position is aligned.
One of main causes of displacement of the superimposing position is change in the velocity of the electrophotographic photoreceptor, the electrophotographic photoreceptor belt, the sheet feeding belt or the intermediate transferring belt, etc.
In order to reduce this disadvantageous change in velocity of the electrophotographic photoreceptor, a method has been proposed in which a rotary encoder is coupled to the rotary shaft of the electrophotographic photoreceptor or the rotary shaft of the intermediate transferring belt. In addition, the method includes the calculation of a controlled variable based on a deviation between a rotational velocity of the electrophotographic photoreceptor obtained from the encoder and a desired velocity. Finally, the method includes controlling the rotational velocity of the electrophotographic photoreceptor based on the deviation (see for example Japanese laid-open patent applications 2001-75324 and 2004-53882).
On the other hand, a different method has been proposed in which a rotary encoder is coupled to a rotary shaft of an intermediate transferring belt in order to obtain a rotational velocity signal based on an edge cycle, a count value and an output by the rotary encoder. Further the method includes calculating moving position information of the intermediate transferring belt from a detection signal detected by a mark sensor which detects scales placed on the intermediate transferring belt along with its moving direction at a predetermined interval and calculating desired position data based on the rotational velocity and the moving position information. Finally, the method includes providing feedback on the desired position data from the feedback control system (see for example Japanese laid-open patent application 2006-160512).
Moreover, an additional method has been proposed in which two mark sensors are placed a predetermined distance apart and are used to detect scales placed on an intermediate transferring belt in addition to a moving direction of the intermediate transferring belt at a predetermined interval. Further the method describes calculating a phase shift based on a detection signal of each mark sensor, which is edge cycle and generating a profile indication of pitch error on marks per rotation cycle based on the sequentially-calculated phase shift. In addition, the method includes generating mark pitch correction data for one rotation cycle and adjusting desired position data based on the mark pitch correction data (see for example Japanese laid-open patent application 2006-139217).
Positioning with high accuracy can be accomplished by using a drive control as is mentioned above. However, when using a tandem type color image forming device, for example, it would be necessary to control many rollers so as to obtain an image with high accuracy. Many motors would need to be controlled, such as a number of drive motors for four photosensitive bodies and an intermediate element, a drive motor for a second transferring belt, a drive motor for a fixation belt or a drive motor for a resister roller that determines the head position of paper and delivers the paper or the like. If these drive motors were to be controlled using a CPU, heavy computation would be required. As a result, it would be necessary to use either a plurality of CPUs or a high-speed CPU resulting in significant cost pressure. The drive control of the electrophotography image forming system is the basis of equal velocity control, but it is desirable to use tracking control to a desired ramp function so as to prevent position displacement which causes image and color drift. Using an encoder pulse count as a rotation position for position control has been generally used, but it has been difficult to equip a mass-produced machine with an encoder with high-resolution and high-accuracy. Thus, the method shown in the references has low cost, however, this method also has low resolution requiring high-speed/massive computation in order to compute a velocity from an edge cycle of a pulse output from an encoder.